U.S. Pat. No. 5,521,722, the content of which is incorporated herein by reference in its entirety, discloses an apparatus for handling digital representations of security documents, in particular of banknotes, which apparatus is intended to facilitate computer-aided design and manufacture of such security documents. According to U.S. Pat. No. 5,521,722, individual sets of design features (referred to as “layers”) making up the composite security design of the security document are stored as individual digital images made of pixels which can be overlaid to build a composite image of the composite security design of the security document. More precisely, U.S. Pat. No. 5,521,722 teaches to store image content and colour content of each relevant “layer” in separate memories and provides an elaborate, but complex, colour generator for generating colour data defining, independently of the image content data, the colour of each pixel of each image or combination of images of the relevant “layers”. A processor selectively combines the image content data and the generated colour data to enable selected images to be viewed separately or in combination, in particular for colour proofing purposes.
The layering structure of U.S. Pat. No. 5,521,722 allows for an individual definition (and modification as the case may be) of each relevant “layer”, i.e. each set of design features is defined in an independent manner, thereby facilitating edition or modification of any “layer” if desired. Measures are further contemplated to provide production tolerance parameters such that the designer can view a particular document when “layers” move laterally within tolerance bands. This is achieved by causing the specified image (or images) to be displaced relative to one another. This ability is however limited to simple translational movements of one image or “layer” with respect to another. While this solution may replicate possible mis-registration of design features which are inherent to the production of security documents, such replication is however not properly reflecting the actual variations which can be encountered in practice during the production of security documents.
German Patent Publication No. DE 10 2004 045 169 A1 (which corresponds to International Patent Publication No. WO 2006/032375 A2) discloses a method for the layout and checking of value documents, in particular banknotes. According to this method, a design of the value document is generated by means of a CAD system, which design comprises several features that are described by CAD data. Such CAD data, which is representative of the design of the value document, is checked as to the suitability of the features for an automatic checking, i.e. by means of a processing machine equipped with sensors designed to check the relevant features. In other words, this method is directed to the appropriate design of machine-readable feature which can suitably be detected by automatic processing machines. This method is based exclusively on the CAD data describing the relevant features of the design of the value document, but does not as such replicate or take into account the actual variations which occur in practice during the actual production of security documents.